Draft gear assemblies are widely used in the railroad industry to provide protection to a railway car by absorbing shocks in both draft and buff conditions. They are installed in alignment with a railway car center sill having a pair of front stops and a pair of opposed rear stops that form a draft gear pocket and cooperate with a separate yoke member attached to a coupler of such railway car. It is well known that various railroads now use a standard draft gear pocket of 24.62 inches in length. As a result, it has been mandated that draft gear assemblies of different designs must fit into such standard draft gear pocket.
It has been further mandated and accepted to provide a standard draft gear assembly for use with a 24.62 inch long pocket which is capable of 3.25 inch travel in both buff and draft directions.
Lately, draft gear assemblies having an integrated yoke have been gaining acceptance in various railway applications. The draft gear assemblies with an integrated yoke have a number of advantages. One advantage is that they fit into a smaller pocket and its adjacent areas in the freight railway car or provide for a higher shock absorbing capacity and longer travel when installed into a standard 24.625 inch long pocket.
Another advantage is that they offer reduced weight and can be delivered from a manufacturer in a fully assembled condition ready for immediate installation and reduce the need for a railroad to procure a separate yoke and shock absorbing member.
Related patent applications teach one type of draft gear assembly with an integral yoke that utilizes a friction-type cushioning and release mechanism. A compressible cushioning element of such friction-type draft gear assembly is positioned within the rear portion of the housing, while a friction cushioning element is disposed in the front portion of the housing. A spring release mechanism for continuously urging the friction cushioning element outwardly from the compressible cushioning element thereby releasing such friction cushioning element after compression of such draft gear. The compressible cushioning element is typically either of an all coil spring configuration as taught in U.S. Pat. Nos. 5,152,409, 5,529,194 and 5,590,797 or of a coil spring and hydraulic assembly combination as taught in U.S. Pat. No. 3,368,698.
U.S. Pat. No. 6,446,820 to Barker et al. teaches another type of draft gear assembly with an integral yoke that has a front resilient compressible elastomeric pad stack and a coupler follower disposed within the yoke portion and a rear resilient compressible elastomeric pad stack disposed intermediate the rear portion of the yoke and the rear follower. A center rod extends through the yoke, the rear resilient compressible elastomeric pad stack and the rear follower.
It has been accepted that, due to wear, the yoke portion must be reconditioned about every 8 years, while the remaining housing portion, particularly in the friction-type draft gear assemblies may be reconditioned about every 16 years. Therefore, a disadvantage of the friction-type draft gear assemblies with an integrated yoke is that the entire assembly must be sent back to the manufacturer for reconditioning thus increasing the complexity and cost of such reconditioning.
It has been further accepted that coupler types presently in use vary between different railroads and car manufacturers with E-shank, F-shank and rotary shank couplers being the most widely used coupler types. Therefore, another disadvantage of the draft gear assembly with an integral yoke member is that it must be configured for use with a particular type of coupler which increases the complexity and cost to interchange the cars with different couplers within a train consist.